Questions tagged [geophysics]

Geophysics is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment.

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Why do we measure eustatic sea-level from the center of earth?

Earth is rotating so it has a ellipsoidal shape. The measurement will therefore be different from equator and pole. So why do we measure eustatic sea-level from the center of earth?
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High-resolution laterolog array tool

Does anybody know if it is necessary to apply corrections to the reading given by this logging tool? Corrections such as bed thickness, borehole diameter, invasion, etc.? If so, is there anywhere I ...
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What are the striations or ridges in the eastern Pacific Ocean?

Messing around on Google Earth recently I noticed a number of striations in the Eastern Pacific. These appear in an East-West orientation and seem to start on the North and South American continental ...
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Does dirt compact itself over time? If so, how does this happen?

If I were to bury something 10 feet (~3 metres) underground, with loose soil on top, would the ground naturally compact itself over time, until whatever I had buried has dirt tightly pressing against ...
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What is the mass of our planet's atmosphere, hydrosphere, and cryosphere combined?

What is the mass of our planet's atmosphere, hydrosphere, and cryosphere combined? How accurate can our estimates be?
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131 views

Mechanism for Pluto's young surface

According to recent reports (e.g. in Nature), Pluto is geologically active. It has some mechanism by which it has "recycled" its surface. I originally thought we had a similar case to Jupiter's moon ...
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Is it dangerous to live in Seattle due to the earthquakes?

I'm considering a move/vacation to Seattle, and I'm concerned it may be dangerous due to the risk of an earthquake?
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572 views

petrophysical crossplots

I recently developed a computer program that generates some petrophysical and elastic parameters from well logs such as water saturation and hydrocarbon saturation, bulk volume, irreducible water ...
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State of Stress in rotated 2D system

I'm working on the rotation of the state of stress using the book Geodynamics of Turcotte page 101. The 2D coordinate system $x'$ and $y'$ is inclined at an angle $\phi$ with respect to the $x$, $y$ ...
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What would change if our earth lacks mountains?

I just asked myself what is the role of the mountains on our planet earth? Well there's a well known role for the climate and weather. But is there a kind of physical or geological role? What would ...
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Can rocks have pressure signatures?

Since rocks can have magnetic signatures, as is the case with paleomagnetism, can they store past pressures also? For example, when researchers are trying to determine past ocean levels, they ...
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1answer
125 views

How to define the force at the base of an oceanic crust

In the book of Turcotte and Schubert, Geodynamics I'm trying to solve problem 2.8. The pressure in the water, in the oceanic crust, and in the mantle beneath the oceanic crust are (from equation 2.19,...
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Available Matlab code to design Seismic Colored Inversion Operator?

I want to apply seismic colored inversion technique to my datasets. Is there a Matlab code available that I can easily use? Are there any other recommended codes to apply seismic colored inversion?
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Why is it necessary in seismic imaging to calculate an image of reflection coefficients when one of the inputs is the velocity model?

Note: I'm not at all an expert in this field. I read in the first few pages of Robein (2010; Seismic Imaging, A Review of the Techniques, their Principles, Merits and Limitations, EAGE) that both ...
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Should RTM amplitudes (pre- and post-stack) be related to rock physics properties?

There is as huge uplift in the image quality near and under salt bodies (e.g. the Middle Miocene of the deepwater Gulf of Mexico) by using reverse time migration or RTM. We can now make accurate ...
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1answer
95 views

Querying Seismic Databases

I'm trying to find 3-component records of the P-wave arrivals of a variety of earthquakes at seismic stations (specific earthquakes or stations aren't important, I just want a small library of these ...
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Publicly-available real-time world-wide seismographic information?

Is there a list of websites supplying real time seismographic information for around the world? I could find for specific places. But I'm looking for a list so I can check for anywhere (providing, of ...
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Is it true that earthquakes are not felt in a cave?

I took a tour of a cave in northern California last weekend. The tour guide asked us, "If an earthquake occurred, what would we feel in here?" My answer was, "fear," but she said we would feel ...
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What are the challenges in predicting lithology directly from acoustic impedance?

Seismic inversion methods help to visualize the subsurface layers of the earth in terms of petrophysical properties (e.g. impedance). Still some geophysicists use the final inverted impedance model in ...
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Discrete Slant Stack on seismic data

In the formula for slant stacking (tau-p transform) a substitution t=tau+d/v is made. If we consider the substitution as a vector equation then how can vector d/v ...
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5answers
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Why does New Zealand and cold countries have volcanoes?

I understand that volcanoes are caused by the heat that causes high intense pressure below the Earth's surface. This intense pressure gets released and causes magna which becomes hot lava to flow out ...
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2answers
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Impact craters vs volcanic explosions on Mars

A maar is a shallow volcanic crater with steep sides that is surrounded by tephra deposits. The tephra deposits are thickest near the crater and decrease with distance from the crater. Source: http://...
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Mars maar craters explosive style formation gravitational effect

"Maars usually form when magma rises within a fissure and interacts with groundwater. If groundwater ceases to interact with magma at times during the eruption, continued magma ascent to the surface ...
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What is the meaning of seismic spectral blueing?

What is the meaning of seismic spectral blueing? Please cite any good introductory materials if possible.
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Books for learning applied seismic geophysics

I am a software developer trying to learn applied geophysics. Specifically I am interested in seismic attributes. I have a strong background in mathematics and signal processing and therefore grasp ...
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How do I extract seismic amplitude on an interpreted horizon?

It seems that seismic amplitude extracted on an interpreted horizon is good for showing channels. E.g.:http://seismicatlas.org/entity?id=98a83c60-ea81-47cc-9304-6041f6ec5277. It seems that often the ...
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380 views

How are the ZNE, ZRT and LQT coordinate systems defined?

I'm confused about the direction of Z (upward or downward?), R (outward or toward the source?) and T.
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Why is continental crust less dense than oceanic?

Why is it that continental crust is less dense than oceanic, where in fact continental crust is thicker than oceanic crust?
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Simulating the earths crust

I would like to create a computer simulation which would fold two plane-ish surfaces into two crumpled-ish surfaces. This in order to simulate the earths crust movement and collisions resulting in ...
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538 views

Stochastic seismic inversion

Could anyone recommend a free and reliable software capable of Stochastic seismic inversion for my project? am aware that Petrel is capable of Genetic inversion based on a non-linear multi-trace ...
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1answer
2k views

How does one determine the optimum offset in a seismic survey?

I was going through a report on MASW (Multi Station Analysis of Surface Wave) and found this "To avoid the aliasing in the space domain, geophone spacing (Δx) needs to be less than half of the ...
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What are the fields in Petrel's IESX seismic horizon file?

I have a text file containing 23 seismic horizons from Petrel, Schlumberger's seismic earth interpretation and modelling tool, using the 2D IESX format. Here are the first few rows: ...
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843 views

Why do deviated wells show poor correlation to seismic data?

Well correlation and calibration is an important step in any type of seismic inversion. In order to obtain a good broadband frequency model, the synthetics should be correlated with original seismic ...
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2answers
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The relation between the magnitude and duration of earthquake

I am asking this question in reference to the recent earthquake that struck Nepal last month. I read that the magnitude 7.8 richter scale earhtquake would have caused more damage had it lasted for ...
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4answers
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Are the oceans rising or the continents going down? How can we know?

The century old sustained rising of oceans, at a rate of 2-4 mm/y, remains a unexplained phenomenon; there is no correlation with temperature variations, so it is not due to the thermal variation of ...
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What ice phenomenon are we seeing in this video?

I don't know what this YouTube video shows, but it appears to be half glacier and half "the blob." It almost appears to be "growing" although I assume it's being pushed somehow. Can someone tell me ...
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1answer
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How should I choose the block size in constrained model-based inversion?

In constrained model based inversion, block size (in ms) is one of the inversion parameters. Specifying the block size value in the software divides the pseudo-velocity log into that number of layers ...
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1answer
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Should one extract wavelet from seismic or well log for the generation of synthetic traces?

Synthetics are generated by convolving reflectivity series with the known wavelet. I have seen most of the wavelet are extracted from seismic data itself. Is there any hard and fast rule, or can one ...
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1answer
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Flexure of a viscous lithosphere - derivation

I have been trying to figure out solution for the fourth order differential equation of flexure for a viscous plate. The fourth order differential equation for a viscous plate is given as $$Dv*\...
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What is the geothermal potential of a volcano?

If there were lots of geothermal plants—even mobile ones—near a volcano, how much power could this provide? Could the sapping of some of the heat energy make the volcano less likely to erupt?
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Predicting earthquakes using disturbances in DTH TV transmission

It is said that before an earthquake happens, a viewer experiences disturbances in DTH TV transmission in the form of distorted images on the screen which automatically correct after a few seconds. ...
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4answers
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Are there any other earthquake magnitude scales other than Richter's?

There are sometimes confusion about the magnitude of Earthquakes. What scales, other than Richter's, are used to measure the magnitude of an earthquake? Is there a scale where magnitude 9.0 is ...
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1answer
627 views

Why do most seismic inversion methods ignore high frequencies?

Different post-stack inversion methods such as model based, sparse spike, colored and recursive inversion methods use high cut frequency impedance logs (low frequency) and mid-frequency seismic trace ...
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280 views

Hydrocarbon potential in Ganges Brahmaputra delta

According to Curray (1991): Total sediment thickness beneath the [Ganges–Brahmaputra delta] southeast of the hingezone exceeds 16 km... Considering a normal geothermal gradient and data for oil ...
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1answer
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Is Iceland an example of a hot-spot overlying a mantle plume?

Iceland has been cited as the location of a hot-spot overlying a mantle plume (similar to that of the Hawaii chain in the Pacific), though for some time this model has been challenged (see Gillian ...
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203 views

Incised valleys and hydrocarbon potential

The Wikipedia page on sequence stratigraphy states: Sandstone bodies associated with incised valleys are good hydrocarbon reservoirs. Can anyone elaborate on this statement and the reason behind ...
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Why does sea level correspond to boundary between oceanic and continental crust?

Is it a coincidence? the first is determined by the amount of water on the Earth and the second comes from evolution of tectonic plates. Still, oceans seem to fill exactly the oceanic crust.
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Dependence of solar irradiation through the atmosphere on Sun's altitude

I want to show that the higher the Sun's altitude, the higher the solar irradiation through the atmosphere, through simple experiments. However, I don't have the instrument that measures irradiation. ...
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1answer
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Why does part of the P-wave convert into a S-wave with an increase of incidence angle?

With the increase of incidence angle, a portion of a P-wave converts into a S-wave, how does this behaviour occur?
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How do we convert the seismic trace wavelet to zero phase which is in mixed phase?

As we know the mixed phase data would not give the "real TWTT" through the medium. We need a zero-phase wavelet that can directly correspond to the time taken to travel in a given media. So my ...